Drawing with DNA: genetic code makes complex shapes

Scientists have developed a way of crafting DNA into complex shapes such as letters of the alphabet, symbols and even smiley faces. The nanotechnology may one day be able to create customised DNA structures that can carry therapeutic drugs to specific sites in the human body without triggering an immune response.

The research, published in Nature, builds on a previous concept called DNA origami in which long stretches of single-stranded DNA are folded into 3D structures and held in place using short DNA 'pins'. It was hoped that this technique could create customised carriers capable of shuttling drugs around the body. However, the long DNA strands were taken from a virus and therefore structures created using this method are likely to be attacked by the body's immune system.

Scientists from Harvard University in the US may have got around this by developing a technique that uses synthetic DNA. Their shape-building method involves the creation of a set of building blocks — or 'tiles' - that are carefully selected to build specific shapes.

Each tile comprises a single DNA strand of just 42 letters designed to fold into a specific shape. A tile can connect to four neighbouring tiles as long as they share enough similarities in their DNA sequences. Five interconnecting tiles form a 'pixel' with the final customised structure made of up to 310 pixels. Once a library of unique tiles has been synthesised, an indeterminate number of shapes can be made simply by leaving different tiles out.

'Each tile acts like a Lego block', explained Dr Peng Yin, the lead scientist on the project. 'Once you have a pre-synthesised library, you don't need any new DNA designs. You just pick your molecules'.

Each tile measures just seven by three nanometres (a nanometre is one billionth of a metre) and construction of the final structures requires the help of a specially-designed robot. The desired shape is drawn onto a graphical interface and the robot selects and mixes the strands to create the shape, a process that takes about an hour. To demonstrate the technique, the scientists re-created well known shapes including alphabet letters and smiley faces.

The technology is in its early stages and Dr Yin stresses that 'any technological applications are highly speculative'. He did acknowledge, however, that the synthetic DNA structures 'could be made to be highly biocompatible'.

Dr Paul Rothemund, who invented the original DNA Origami method at the California Institute of Technology, said of this new research: '[These] findings remind us that we are still just apprentice DNA carpenters, and will embolden others to mix hundreds of DNA strands together against prevailing wisdom. The results will probably surprise us'.